Atoms — Physics STD 12 Science — Question

An electron moves with a constant velocity v in a uniform magnetic field B, parallel to the direction of the magnetic field. The force acting on electron is:

Internal forces can change:

1. The linear momentum but not the kinetic energy.
2. The kinetic energy but not the linear momentum.
3. Linear momentum as well as kinetic energy.
4. Neither the linear momentum nor the kinetic energy.

A positive point charge Q is brought near an isolated metal cube.

1. The cube becomes negatively charged.
2. The cube becomes positively charged.
3. The interior becomes positively charged and the surface becomes negatively charged.
4. The interior remains charge free and the surface gets nonuniform charge distribution.

As shown in the figure, charges +q and -q  are placed at the vertices B and C  of an isosceles triangle. The potential at the vertex A is

(a) .

(b) Zero

(c)

(d)

Which quantity decrease in step-down transformer ?

The capacity of a parallel plate condenser is 10μF  without dielectric. Dielectric of constant 2 is used to fill half the distance between the plates, the new capacitance in μF is

(a) 10

(b) 20

(c) 15

(d) 13.33

A magnetic field can be produced by :

In the circuit shown in figure, the current drawn from the battery is 4A.  If 10 W resistor is replaced by 20 W resistor, then current drawn from the circuit will be

(a) 1 A

(b) 2 A

(c) 3 A

(d) 0 A

With increase in temperature the conductivity of:

In a region of constant potential: